(1) Field of the Invention
The present invention relates to a compact self-ballasted fluorescent lamp having an arc tube and a holder, the arc tube being made of a glass tube whose at least one part is bent, ends of the glass tube being respectively provided with an electrode equipped with a filament coil, and the holder being provided with insertion openings through which the ends of the glass tube are inserted and held.
(2) Related Art
In the present energy-saving era, compact self-ballasted fluorescent lamps started to become pervasive as light sources alternative to incandescent lamps. One example of such compact self-ballasted fluorescent lamps is shown in FIG. 1. This compact self-ballasted fluorescent lamp has an arc tube 910 formed by bending a glass tube 911 in a double spiral configuration, and a holder 920 made of resin and holds this arc tube 910. This holder 920 stores therein an electronic ballast for lighting the arc tube 910. At one end of the holder 920, a base 924 that is the same type as for the incandescent lamps is fixed. Each end of the glass tube 911 is provided with an electrode equipped with a filament coil.
The arc tube of this compact self-ballasted fluorescent lamp is formed by bending a glass tube at the substantial middle, and winding the glass tube from the substantial middle up to the both ends, around an axis of spiral (hereinafter, this axis is referred to as “spiral axis”) (in FIG. 1, the spiral axis being in the vertical direction and corresponding to the axis of the base). Such an arc tube is advantageous over an arc tube that has ends of the glass tube running parallel to the spiral axis, or over an arc tube formed by connecting three U-shape glass tubes (so to speak, three U-shape arc tube), in that it can be made smaller for the same amount of light emission (refer to Japanese Patent Publication H9-17378).
The mentioned holder 920 that holds the arc tube 910 formed by winding the glass tube up to the ends includes: a holding resin member 925 with a cylindrical shape having a closed bottom and has, at the bottom wall of the cylindrical shape, insertion openings 922 through which ends of the glass tube 911 are inserted; and a resin cover 923 to be fit to the outer surface of the circumference of the holding resin member 925. The ends of the glass tube 911, having been inserted into the insertion openings 922, are attached to the holding resin member 925 of the holder 920, by means of a silicone resin and the like.
Meanwhile, a life test was conducted for a compact self-ballasted fluorescent lamp that uses the arc tube 910, whose glass tube 911 is wound around up to its ends. As a result, at the ending of the lamp life, deformation due to heat was observed at areas of the holding resin member 925 and of the resin cover 923, the areas corresponding to where the filament coils are placed within the glass tube 911.
More specifically, when a life test is conducted by lighting the compact self-ballasted fluorescent lamp with the base 924 directed downward (hereinafter, this way of lighting is referred to as “downward illumination”), Sa area of an end wall 921 of the holding resin member 925 is deformed due to heat, as shown in FIG. 1. This Sa area is the area that positions directly over a filament coil of the glass tube 911.
If a life test is conducted by lighting the compact self-ballasted fluorescent lamp with the base 924 directed in the lateral direction (hereinafter, this way of lighting is referred to as “lateral illumination”), Sb area of the circumferential wall of the resin cover 923 is deformed, as shown in FIG. 1. Deformation was most pronounced when the compact self-ballasted fluorescent lamp is laid so that the filament coil provided in one of the ends of the glass tube 911 positions at the top.
Note that FIG. 1 shows the compact self-ballasted fluorescent lamp after ending of the life test, and is for both of the life test in the downward illumination, and the life test in the lateral illumination, for convenience purpose.